Dissertations / Theses on the topic 'Joint Spatial Division and Multiplexing'

L'évolution technologique rapide introduite par les générations des communications sans fil a été motivé par l'émergence de services à fortes valeurs ajoutées nécessitant toujours plus de débit mais aussi une couverture bien meilleure, ceci conduisant in fine à utiliser le spectre plus efficacement. Pour ce faire, la Sixième Génération (6G) des réseaux sans fil, pourra s'appuyer sur des technologies innovantes telles que les Surfaces Intelligentes Reconfigurables (RIS) et le Massive Multiple Input Multiple Output (mMIMO), ces dernières pourraient y jouer des rôles cruciaux. Cette thèse explore l'intégration des RIS dans les systèmes mMIMO dans le but d'améliorer les performances des communications sans fil.La première partie de la thèse, porte sur l'application de la Division et Multiplexage Spatiaux Conjoint (JSDM) dans les systèmes MIMO multi-utilisateur assistés par une RIS. En positionnant stratégiquement les RIS près des utilisateurs dont les canaux directs avec la station de base (BS) sont dégradés, nous développons des solutions pour adapter les algorithmes de regroupement d'utilisateurs JSDM en prenant en compte les configurations RIS. Cette approche exploite les signatures spatiales et introduit une étape de précodage supplémentaire pour le JSDM, atténuant les effets néfastes du canal RIS-BS, améliorant ainsi significativement le débit somme et la couverture du système. Les solutions proposées démontrent le potentiel des RIS dans le but d'améliorer la couverture en établissant des liens robustes entre la BS et les utilisateurs, améliorant ainsi les performances globales du réseau.La deuxième partie aborde le défi des canaux BS-RIS de faible rang en proposant un système RIS distribué. En déployant des RIS intermédiaires entre la BS et une RIS principale, nous créons un canal intégré ayant un rang amélioré, et adapté pour servir plusieurs utilisateurs simultanément. La performance de ce paradigme est évaluée en prenant un précodage Regularized Zero Forcing (RZF) et le JSDM,les décalages de phase des signaux, par les RISs, y sont optimisés par un algorithme de montée de gradient projeté. Les résultats démontrent des améliorations de performance substantielles, même dans des conditions de perte de chemin élevée, due à la double réflexion par les RISs. Cette stratégie de déploiement augmente non seulement le gain de multiplexage spatial, mais aussi réduit la complexité de l'estimation de l'information sur l'état du canal.Dans la dernière partie, nous introduisons un nouveau cadre coopératif qui permet aux RIS de changer dynamiquement de rôle entre principal et intermédiaire. Cette double fonctionnalité permet des réponses flexibles d'une part aux évolutions environnementales et d'autre part aux besoins des utilisateurs, en optimisant dynamiquement les gains de multiplexage spatial ainsi que la couverture. La conception d'un codebook de focalisation pour chaque RIS et la mise en place de la politique de planification dynamique basées sur la théorie de l'optimisation de Lyapunov permettre de maintenir la stabilité des files d'attente de données des utilisateurs et d'optimiser les débits à long terme. La planification coopérative garantit que le gain de multiplexage spatial est dynamiquement transféré d'une région à une autre, offrant des performances MU-MIMO fiables tout au long de la cellule.À travers des études analytiques et de simulation rigoureuses, cette thèse fournit des perspectives pratiques sur le déploiement des RIS, soulignant le potentiel de la technologie RIS dans le but d'améliorer significativement les performances de communication sans fil. Les résultats soulignent l'impact important des RIS sur l'efficacité du réseau, la couverture et l'expérience utilisateur, ouvrant la voie à la prochaine génération de systèmes de communication sans fil
The rapid advancement of wireless communication technologies has been driven by the increasing demand for higher data rates, better coverage, and more efficient spectrum utilization. As we transition towards the Sixth Generation (6G) of wireless networks, innovative technologies such as Reconfigurable Intelligent Surfaces (RIS) and Massive MIMO (mMIMO) are set to play crucial roles in meeting these demands. This thesis explores the integration of RIS with mMIMO systems to enhance wireless communication performance, particularly in Multi-User MIMO (MU-MIMO) scenarios.In the first part of the thesis, we focus on the application of Joint Spatial Division and Multiplexing (JSDM) in RIS-aided MU-MIMO systems. By strategically positioning RIS near users with weak direct Base Station (BS) channels, we develop solutions to adapt JSDM user clustering algorithms for RIS configurations. This approach leverages spatial signatures and introduces an additional precoding stage to JSDM mitigating the adverse effects of the RIS-BS channel, significantly improving the sum rate and system coverage. The proposed solutions demonstrate the potential of RIS to enhance coverage by establishing robust links between the BS and users, thereby improving overall network performance.The second part of the thesis addresses the challenge of low-rank BS-RIS channels by proposing a distributed RIS system. By deploying intermediate RISs between the BS and a main RIS, we create an integrated channel with enhanced rank characteristics, suitable for serving multiple users simultaneously. The performance of this paradigm is analyzed under Regularized Zero Forcing (RZF) and JSDM precoding, with RIS phase shifts optimized through a projected gradient ascent algorithm. The results demonstrate substantial performance improvements, even under high double reflection path-loss conditions. This innovative deployment strategy not only increases the spatial multiplexing gain but also reduces the complexity of channel state information (CSI) estimation.In the final part, we introduce a novel cooperative RIS framework that allows RISs to dynamically switch roles between main and intermediate. This dual functionality enables flexible responses to changing environmental conditions and user requirements, optimizing spatial multiplexing gains and overall coverage. We design a focusing codebook for each RIS and develop dynamic scheduling policies based on Lyapunov optimization theory to maintain user data queue stability and optimize long-term user data rates. The cooperative scheduling framework ensures that the spatial multiplexing gain is dynamically shifted from one region to another, providing reliable MU-MIMO performance throughout the cell.Through rigorous analytical and simulation studies, this thesis provides practical insights into the deployment of RIS in future 6G networks, highlighting the potential of RIS technology to significantly enhance wireless communication performance. The findings underscore the transformative impact of RIS on network efficiency, coverage, and user experience, paving the way for the next generation of wireless communication systems

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California
An advanced electro-optic hybrid rotary joint (EOHRJ) has been developed in Phase II of an AF SBIR effort with Physical Optics Corporation (POC) to replace cable wrap structure for multi-channel rotation-to-fixed (RTF) signal transmission. The EOHRJ meets AFFTC and other range special needs with a generic, high performance, rotary joint solution. At the moment, we have successfully installed and tested the EOHRJ on our KTM tracker system with the following capabilities: 1) able to accommodate hundreds of transmission channels, including electrical power, control, feedback, and low-speed signals; 2) able to accommodate multiple channel, high data rate (over gigabits per second), and bi-directional signal transmission; 3) able to be reliable for harsh environmental operation, adaptive to stringent sized requirement, and accommodating existing electrical and mechanical interfaces. The completed EOHRJ contains three uniquely integrated functional rings. The first and the outmost one is power ring, which provides RTF transmission channels for over 50 high voltage and high current channels. The second and the middle one is low speed electrical signal ring, which provides RTF transmission for over hundred control, feedback, and low speed data signals. The third and the inmost one is optical fiber slip ring, which, incorporating with current advanced signal multiplexing technologies (either time division or wavelength division multiplexing ) is able to provide multiple channel, high data rate, and bi-directional signal transmission. At the moment, the prototype module of the tree-layer EOHRJ has been successfully assembled in Air Force’s tracker system, and is providing a satisfactory performance. This paper presents our joint work on this project.

Part A: Spatial Mode-Division Multiplexing: As the capacity limits of single-mode optical fibre are being approached, attention has shifted to few-mode fibre. Increasing capacity then amounts to independently exciting and detecting the various spatial modes, in what is known as spatial mode-division multiplexing. In this approach each mode acts as a different data channel. The independent excitation and detection of the individual spatial modes however remains a major technological challenge, and at present experimental demonstrations have relied on lossy bulk free-space optics. In this thesis, simpler and more compact waveguide-based alternatives are proposed and analysed. Firstly, it is shown that asymmetric Y-junctions can be used to adiabatically multiplex/demultiplex the modes of polarization-maintaining or elliptical-core few-mode fibre. Analytical models describing the mode-selective functionality of these devices are developed and it is shown numerically that the performance is largely independent of wavelength, hence permitting wideband wavelength-division multiplexing. Another class of compact waveguide-based devices suitable for mode-division multiplexing are mode-selective couplers. Coupled mode theory is used to develop an analytical model of these devices, and it is shown that specific three-core variants permit demultiplexing of asymmetric higher-order modes irrespective of modal orientation. The wavelength-dependence of these couplers is however shown to limit their use in wavelength-division multiplexed systems. In order to solve the wavelength-dependence issue of these couplers, adiabatic tapers can be introduced into the cores. Such structures are referred to as tapered velocity mode-selective couplers, and unlike standard directional mode-couplers, these novel devices do not require precise phase conditions to be satisfied over an extended length. For this reason they permit ultra-wideband mode-division multiplexing of few-mode fibre. It is again shown that three-core variants of these tapered couplers can permit mode-orientation independent decoupling. These devices are numerically analyzed, and their successful fabrication using the femtosecond-laser direct write technique is also reported. These developments could play a very significant role in future high-capacity telecommunications. Part B: Advanced Distributed Fibre Sensing Techniques: Distributed optical fibre sensing techniques are invariably plagued by trade-offs between the performance metrics of range, spatial resolution and measurement bandwidth. This is especially true for the most well-known frequency domain and time domain fibre sensing techniques of optical frequency domain reflectometry (OFDR) and optical time domain reflectometry (OTDR), respectively. What is needed to lessen the performance trade-offs, is a hybrid technique using both time and frequency domain signal analysis. The merging of the realms of time and frequency domain fibre sensing is demonstrated in this thesis using a range-gated variant of OFDR. The range-gating is achieved by time stamping the optical signal using high-frequency pseudorandom noise phase modulation, also known as digitally enhanced interferometry. The merging of digital interferometry and OFDR is referred to as digitally enhanced OFDR. This technique permits orders of magnitude reduction in the required sampling rates of OFDR, and overcomes the range ambiguity inherent in OFDR when sensing over multiple frequency sweeps. The latter feature means the technique can be used for ultra-high (e.g. acoustic) bandwidth sensing without sacrificing range or spatial resolution.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada
Current ground-based tracking systems at the DoD test and training ranges require transmission of a variety of signals from rotating platform to fixed control and process center. Implementation of commercial off the shelf (COTS) solution for transmitting high-speed, multiple-channel data signals over a rotational platform prompt the development of an advanced electro-optic hybrid rotating-to-fixed information transmission technology. Based on current demand, an Air Force-sponsored Small Business Innovative Research (SBIR) contract has been awarded to Physical Optics Corporation (POC) to modify existing tracking mounts with a unique electro-optic hybrid rotary joint (EOHRJ). The EOHRJ under current development is expected to provide the following features: 1) include a specially designed electrical slip-ring, which is able to accommodate hundreds of transmission channels, including electrical power, control, feedback, and low-speed data signals; 2) include an optical fiber slip-ring which, by incorporating with electrical time division mulitplexing (TDM) and optical wavelength division multiplexing (WDM) technologies, is able to provide multiple channel, high data rate (over gigabits per second), and bi-directional signal transmission; and 3) is designed to be reliable for harsh environmental operation, adaptive to stringent size requirement, and accommodating to existing electrical and mechanical interfaces. Besides the military use, other possible commercial applications include on board monitoring of satellite spinners, surveillance systems, instrumentation and multi spectral vision systems, emergency/medical instruments, remote sensing, and robotics.

Les besoins toujours croissants en terme de transfert de données numériques poussent au développement de nouvelles technologies pour accroître la capacité des réseaux, notamment en ce qui concerne les réseaux de fibre optique. Parmi ces nouvelles technologies, le multiplexage spatial permet de multiplier la capacité des liens optiques actuels. Nous nous intéressons particulièrement à une forme de multiplexage spatial utilisant le moment cinétique orbital de la lumière comme base orthogonale pour séparer un certain nombre de canaux. Nous présentons d’abord les notions d’électromagnétisme et de physique nécessaires à la compréhension des développements ultérieurs. Les équations de Maxwell sont dérivées afin d’expliquer les modes scalaires et vectoriels de la fibre optique. Nous présentons également d’autres propriétés modales, soit la coupure des modes, et les indices de groupe et de dispersion. La notion de moment cinétique orbital est ensuite introduite, avec plus particulièrement ses applications dans le domaine des télécommunications. Dans une seconde partie, nous proposons la carte modale comme un outil pour aider au design des fibres optiques à quelques modes. Nous développons la solution vectorielle des équations de coupure des modes pour les fibres en anneau, puis nous généralisons ces équations pour tous les profils de fibres à trois couches. Enfin, nous donnons quelques exemples d’application de la carte modale. Dans la troisième partie, nous présentons des designs de fibres pour la transmission des modes avec un moment cinétique orbital. Les outils développés dans la seconde partie sont utilisés pour effectuer ces designs. Un premier design de fibre, caractérisé par un centre creux, est étudié et démontré. Puis un second design, une famille de fibres avec un profil en anneau, est étudié. Des mesures d’indice effectif et d’indice de groupe sont effectuées sur ces fibres. Les outils et les fibres développés auront permis une meilleure compréhension de la transmission dans la fibre optique des modes ayant un moment cinétique orbital. Nous espérons que ces avancements aideront à développer prochainement des systèmes de communications performants utilisant le multiplexage spatial.
The always increasing need for digital data bandwidth pushes the development of emerging technologies to increase network capacity, especially for optical fiber infrastructures. Among those technologies, spatial multiplexing is a promising way to multiply the capacity of current optical links. In this thesis, we are particularly interested in current spatial multiplexing using the orbital angular momentum of light as an orthogonal basis to distinguish between a few optical channels. We first introduce notions from electromagnetism and physic needed for the understanding of the later developments. We derive Maxwell’s equations describing scalar and vector modes of optical fiber. We also present other modal properties like mode cutoff, group index, and dispersion. Orbital angular momentum is briefly explained, with emphasis on its applications to optical communications. In the second part, we propose the modal map as a tool that can help in the design of few mode fibers. We develop the vectorial solution of the ring-core fiber cutoff equation, then we extend those equations to all varieties of three-layer fiber profiles. Finally, we give some examples of the use of the modal map. In the third part of this thesis, we propose few fiber designs for the transmission of modes with an orbital angular momentum. The tools that were developed in the second part of this thesis are now used in the design process of those fibers. A first fiber design, characterized by a hollow center, is studied and demonstrated. Then a second design, a family of ring-core fibers, is studied. Effective indexes and group indexes are measured on the fabricated fibers, and compared to numerical simulations. The tools and the fibers developed in this thesis allowed a deeper comprehension of the transmission of orbital angular momentum modes in fiber. We hope that those achievements will help in the development of next generation optical communication systems using spatial multiplexing.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California
Spatial multiplexing (SM) systems have received significant attention because the architecture offers high spectral efficiency. However, relatively little research exists on optimization of SM systems in the presence of jamming. In a spatially uncoded SM system, such as V-BLAST, the channel state information is assumed to be unavailable a priori at both transmitter and receiver. Here, Kalman filtering is used to estimate the Rayleigh fading channel at the receiver. The spatial correlation of the jammer plus noise is also estimated, and spatial whitening to reject the jammers is employed in both the Kalman channel estimator and detector. To avoid the exponential complexity of maximum-likelihood (ML) detection, the QRD-M algorithm is employed. In contrast to sphere decoding, QRD-M has fixed decoding complexity of order O(M), and is thus attractive for hardware implementation. The performance of the joint Kalman filter channel estimator, spatial whitener and QRD-M detector is verfied by simulations.

Les deux dernières décennies ont connu une croissance exponentielle de la demande pour plus de capacité dans les réseaux optiques. Cette croissance a été principalement causée par le développement d'Internet et le trafic croissant généré par le nombre croissant des utilisateurs. La fibre optique offre plusieurs degrés de liberté pour augmenter la capacité. La fréquence, le temps, la phase, la polarisation ont déjà été utilisés pour satisfaire la demande de bande passante, ainsi le multiplexage spatial (SDM) reste le seul degré de liberté disponible pouvant être utilisé dans les systèmes optiques afin d'augmenter la capacité. Cependant, les interactions entre les différents canaux spatiaux dans le même milieu de propagation est inévitable. Ces interactions, si elles ne sont pas compensées, entraînent des dégradations qui détériorent les performances du système. À cette fin, des recherches intensives sont menées récemment afin de développer un traitement de signal avancé capable de traiter ces détériorations dans les systèmes à multiplexage spatial. Motivés par le rôle potentiel des fibres optiques multimodes (MMF) dans les futurs systèmes SDM, dans cette thèse, nous présentons des solutions de codage modernes pour réduire la diaphonie non-unitaire qui affecte les modes spatiaux dans les fibres multimodes entraînant une dégradation des performances
In a very fast pace, the last two decades have known an exponential growth in the demand for more optical network capacity, this growth was mainly caused by the built-out of the Internet and the growing traffic generated by an increasing number of users. Since frequency, time, phase, polarization have already been used to satisfy the demand for bandwidth, space-division multiplexing (SDM) remains the only available degree of freedom that can be used in optical transmission systems in order to increase the capacity. However, interactions between spatial channels in the same propagation medium is inevitable. These interactions, if not compensated, result in impairments that deteriorate the system performance. For this purpose, intensive research is being carried out in recent years in order to provide advanced signal processing capable to deal with these impairments in spatial multiplexing systems. Motivated by the potential role of multi-mode fibers (MMFs) in future SDM systems, in this thesis, we present modern coding solutions to mitigate the non-unitary crosstalk known as mode-dependent loss (MDL) that affects spatial modes of MMFs resulting in degraded system performance

With the rapid growth of wireless data demands and saturation of radio frequency (RF) capacity, visible light communication (VLC) has become a promising candidate to complement conventional RF communication, especially for indoor short range applications. However the performance of the system depends on the propagation and type of system used. An optical Orthogonal Frequency Division Multiplexing (O-OFDM) together with multiple input multiple output (MIMO) in different scenario and modulation techniques are studied in the thesis. A novel optical wireless communication (OWC) multi-cell system with narrow field of view (FOV) is studied. In this system the intensity modulated beam from four light sources are used for communication. The system allows beams to be concentrated in specific areas of the room to serve multiple mobile devices with low interference and hence increase system capacity. The performance of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM), direct current biased optical OFDM (DCO-OFDM) and single carrier (SC) modulation are then compared in this system considering single user and multiusers scenarios. The performance of the multi-cell is compared with single cell with wide FOV. It is shown that the capacity for multi-cell system increases with the number of users to 4 times the single user capacity. Also the findings show that multi-cell system with narrow beams can outperform a single wide beam system in terms of coverage area and hence average throughput of about 2.7 times the single wide beam system capacity. One of the impairments in line of sight (LOS) OWC systems is coverage which degrades the performance. A mobile receiver with angular diversity detectors in MIMO channels is studied. The objective is to improve the rank of the channel matrix and hence system throughput. Repetition coding (RC), spatial multiplexing (SMP) and spatial modulation (SM) concepts are used to evaluate throughput across multiple locations in a small room scenario. A novel adaptive spatial modulation (ASM) which is capable of combating channel rank deficiency is devised. Since the receiver is mobile, the channel gains are low in some locations of the room due to the lack of LOS paths between transmitters and receivers. To combat the situation adaptive modulation and per antenna rate control (PARC) is employed to maximise spectral efficiency. The throughputs for fixed transmitters and receivers are compared with the oriented/inclined detectors for different cases. Angular diversity detectors offer a better throughput improvement than the state of the art vertical detectors, for example in ASM angular diversity receiver gives throughput of about 1.6 times that of vertical detectors. Also in SMP the angular detectors offer throughput about 1.4 times that of vertical detectors. SMP gives the best performance compared to RC, SM and ASM, for example SMP gives throughput about 2.5 times that of RC in both vertical detectors and angular diversity receivers. Again SMP gives throughput about 6 times that of SM in both vertical detectors and angular diversity receivers. Also SMP provides throughput about 2 times that of ASM in both vertical detectors and angular diversity receivers. ASM exhibit improvement in throughput about average factor of 3.5 times SM performance in both vertical detectors and angular diversity detectors. As the performance of the system may be jeopardized by obstructions, specular and diffuse reflection models for indoor OWC systems using a mobile receiver with angular diversity detectors in MIMO channels are considered. The target is to improve the MIMO throughput compared to vertically oriented detectors by exploiting reflections from different reflecting surfaces in the room. The throughput across multiple locations in the small room by using RC, SMP and SM approaches is again evaluated. The results for LOS only channels against LOS with specular or diffuse reflection conditions, for both vertical and angular oriented receivers are then compared. The results show that exploiting specular and diffuse reflections provide significant improvements in link performance. For example the reflection coefficient (α) of 0.9 and the antenna separation of 0.6 m, RC diffuse model shows throughput improvement of about 1.8 times that of LOS for both vertical detectors and angular diversity receivers. SM diffuse model shows throughput improvement of about 3 times that of LOS for both vertical detectors and angular diversity receivers. ASM diffuse model shows throughput improvement of about 2 times that of LOS for both vertical detectors and angular diversity receivers. SMP diffuse model shows throughput improvement of about 1.5 times that of LOS for both vertical detectors and angular diversity receiver.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, Dec. 2004.
Thesis advisor(s): Murali Tummala, Roberto Cristi. Includes bibliographical references (p. 69-71). Also available online.

Orthogonal frequency-division multiplexing (OFDM) has been adopted by many broadband wireless communication systems for the simplicity of the receiver technique to support high data rates and user mobility. However, studies also show that the advantage of OFDM over the single-carrier modulation schemes could be substantially compromised by timing or frequency estimation errors at the receiver. In this thesis we investigate the synchronization problem for practical OFDM systems using a system model generalized from the IEEE 802.11 and IEEE 802.16 standards. For preamble based synchronization schemes, which are most common in the downlink of wireless communication systems, we propose a novel timing acquisition algorithm which minimizes false alarm probability and indirectly improves correct detection probability. We then introduce a universal fractional carrier frequency offset (CFO) estimator that outperforms conventional methods at low signal to noise ratio with lower complexity. More accurate timing and frequency estimates can be obtained by our proposed frequency-domain algorithms incorporating channel knowledge. We derive four joint frequency, timing, and channel estimators with different approximations, and then propose a hybrid integer CFO estimation scheme to provide flexible performance and complexity tradeoffs. When the exact channel delay profile is unknown at the receiver, we present a successive timing estimation algorithm to solve the timing ambiguity. Both analytical and simulation results are presented to confirm the performance of the proposed methods in various realistic channel conditions. The ranging based synchronization scheme is most commonly used in the uplink of wireless communication systems. Here we propose a successive multiuser detection algorithm to mitigate multiple access interference and achieve better performance than that of conventional single-user based methods. A reduced-complexity version of the successive algorithm feasible for hardware real-time implementation is also presented in the thesis. To better understand the performance of a ranging detector from a system point of view, we develop a technique that can directly translate a detector�s missed detection probability into the maximum number of users that the method can support in one cell with a given number of ranging opportunities. The analytical results match the simulations reasonably well and show that the proposed successive algorithms allow a base station to serve more than double the number of users supported by the conventional methods. Finally, we investigate inter-carrier interference which is caused by the timevarying communication channels. We derive the bounds on the power of residual inter-carrier interference that cannot be mitigated by a frequency-domain equalizer with a given number of taps. We also propose a Turbo equalization scheme using the novel grouped Particle filter, which approaches the performance of the Maximum A Posterior algorithm with much lower complexity.

In order to meet the ever-growing demand for mobile data, a number of different technologies have been adopted by the fourth generation standardization bodies. These include multiple access schemes such as spatial division multiple access (SDMA), and efficient modulation techniques such as orthogonal frequency division multiplexing (OFDM)-based modulation. The specific objectives of this theses are to develop an effective feedback method for interference management in smart antenna SDMA systems and to design an efficient OFDM-based modulation technique, where an additional dimension is added to the conventional two-dimensional modulation techniques such as quadrature amplitude modulation (QAM). In SDMA time division duplex (TDD) systems, where channel reciprocity is maintained, uplink (UL) channel sounding method is considered as one of the most promising feedback methods due to its bandwidth and delay efficiency. Conventional channel sounding (CCS) only conveys the channel state information (CSI) of each active user to the base station (BS). Due to the limitation in system performance because of co-channel interference (CCI) from adjacent cells in interference-limited scenarios, CSI is only a suboptimal metric for multiuser spatial multiplexing optimization. The first major contribution of this theses is a novel interference feedback method proposed to provide the BS with implicit knowledge about the interference level received by each mobile station (MS). More specifically, it is proposed to weight the conventional channel sounding pilots by the level of the experienced interference at the user’s side. Interference-weighted channel sounding (IWCS) acts as a spectrally efficient feedback technique that provides the BS with implicit knowledge about CCI experienced by each MS, and significantly improves the downlink (DL) sum capacity for both greedy and fair scheduling policies. For the sake of completeness, a novel procedure is developed to make the IWCS pilots usable for UL optimization. It is proposed to divide the optimization metric obtained from the IWCS pilots by the interference experienced at the BS’s antennas. The resultant new metric, the channel gain divided by the multiplication of DL and UL interference, provides link-protection awareness and is used to optimize both UL and DL. Using maximum capacity scheduling criterion, the link-protection aware metric results in a gain in the median system sum capacity of 26.7% and 12.5% in DL and UL respectively compared to the case when conventional channel sounding techniques are used. Moreover, heuristic algorithm has been proposed in order to facilitate a practical optimization and to reduce the computational complexity. The second major contribution of this theses is an innovative transmission approach, referred to as subcarrier-index modulation (SIM), which is proposed to be integrated with OFDM. The key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore, a closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channel is derived. Simulation results show BER performance gain of 4 dB over 4-QAM OFDM for both coded and uncoded data without power saving policy. Alternatively, power saving policy maintains an average gain of 1 dB while only using half OFDM symbol transmit power.

Os sistemas ópticos atuais, baseados em fibras monomodo, operam próximos ao limite teórico da capacidade. Sistemas ópticos baseados em multiplexação modal (Mode Division Multiplexing – MDM) possibilitam o aumento da capacidade do sistema por meio do uso de fibras de poucos modos. Nestes sistemas, a propriedade de ortogonalidade entre os modos propagantes permite que cada modo espacial carregue um sinal óptico específico. O amplificador à fibra dopada com érbio (Erbium-Doped Fiber Amplifier – EDFA) segue fundamental para assegurar a transmissão em longas distâncias. No entanto, devido às distintas distribuições de intensidade dos modos que compõem o sinal de entrada, cada modo experimenta diferentes valores de ganho. Desta forma, o objetivo principal no projeto de EDFAs de poucos modos (Few-Mode Erbium-Doped Fiber Amplifier – FM-EDFA) é determinar os melhores parâmetros opto-geométricos da fibra para produzir uma amplificação eficiente. A metodologia normalmente empregada é baseada na resolução das equações de taxa e de propagação. Nesta tese, é proposta uma metodologia alternativa de projeto de FM-EDFA, baseada em uma nova figura de mérito. Este parâmetro quantifica o nível de inversão da população dos íons na fibra a partir da integral de superposição (overlap integral), considerando tanto o perfil de dopagem da fibra dopada com érbio para poucos modos (Few-Mode Erbium-Doped Fiber – FM-EDF) quanto as distribuições de intensidade dos sinais de entrada e de bombeio. A aplicação desta metodologia permite reduzir, em cerca de 25-40 vezes, o número de resoluções das equações de taxa e de propagação e, consequentemente, diminuir o tempo de processamento e reduzir o esforço computacional. Como consequência da maior velocidade de processamento, torna-se possível a aplicação de métodos de otimização mais rigorosos, permitindo uma busca em um espaço irrestrito de soluções. Especificamente, a partir de uma metodologia baseada em algoritmos genéticos, obteve-se um perfil de dopagem otimizado. É também demonstrado que os perfis com geometria circular exibem melhores características, como excelente desempenho do FM-EDFA e maior facilidade de fabricação. Por meio da análise da figura de mérito, é mostrado que o desempenho do FM-EDFA é afetado pelas características do modo de bombeio. Finalmente, o desempenho de um sistema óptico MDM é avaliado, simulado por meio da integração entre as ferramentas MatLab® e VPItransmissionMakerTM, comprovando a necessidade do projeto de um amplificador específico para sistemas MDM.
Modern optical systems based on single-mode fiber, operate close to the theoretical capacity limit. By using few-mode fibers, optical systems based on modal division multiplexing (MDM) allows increased system capacity. In these systems, orthogonality between the propagating modes allows each spatial mode to carry a specific optical signal. The erbium doped fiber amplifier (EDFA) remains essential to ensure long distance transmission. However, due to the distinct intensity profile distributions of the modes which comprise the input signal, each mode experiences a different value of optical gain. Thus, the main objective in the few-mode EDFA design (FM-EDFA) is to determine the best opto-geometrical fiber parameters in order to produce an efficient amplification. The methodology normally used is based on the simultaneous resolution of the rate and propagation equations. In this thesis, we propose an alternative methodology for the FM-EDFA design, based on a new figure of merit which quantifies the level of population inversion for the Er ions in the fiber, by means of a overlap integral considering both the doping profile of the few-mode erbium doped fiber (FM-EDF) as well as the intensity distributions of the optical signals and pump beams. This methodology reduces, by a factor of 25-40, the number of resolutions of the rate and propagation equations, thereby decreasing processing time and computational effort. As a consequence of the improved processing speed, it becomes possible to apply more rigorous optimization methods in an unrestricted solution space. Specifically, by using a genetic algorithm technique, we obtained an optimized doping profile. It is also shown that profiles with circular geometry exhibit improved features, such as excellent FM-EDFA performance and ease of manufacturing. By analyzing the figure of merit, it is shown that the FM-EDFA performance is affected by the characteristics of the pump mode. Finally, the performance of an MDM optical system is evaluated, by integrating Matlab and VPI simulation tools, to demonstrate the need for specific amplifier designs in MDM systems.

This work concentrates on the application of diversity techniques and space time block coding for future mobile wireless communications. The initial system analysis employs a space-time coded OFDM transmitter over a multipath Rayleigh channel, and a receiver which uses a selection combining diversity technique. The performance of this combined scenario is characterised in terms of the bit error rate and throughput. A novel four element QOSTBC scheme is introduced, it is created by reforming the detection matrix of the original QOSTBC scheme, for which an orthogonal channel matrix is derived. This results in a computationally less complex linear decoding scheme as compared with the original QOSTBC. Space time coding schemes for three, four and eight transmitters were also derived using a Hadamard matrix. The practical optimization of multi-antenna networks is studied for realistic indoor and mixed propagation scenarios. The starting point is a detailed analysis of the throughput and field strength distributions for a commercial dual band 802.11n MIMO radio operating indoors in a variety of line of sight and non-line of sight scenarios. The physical model of the space is based on architectural schematics, and realistic propagation data for the construction materials. The modelling is then extended and generalized to a multi-storey indoor environment, and a large mixed site for indoor and outdoor channels based on the Bradford University campus. The implications for the physical layer are also explored through the specification of antenna envelope correlation coefficients. Initially this is for an antenna module configuration with two independent antennas in close proximity. An operational method is proposed using the scattering parameters of the system and which incorporates the intrinsic power losses of the radiating elements. The method is extended to estimate the envelope correlation coefficient for any two elements in a general (N,N) MIMO antenna array. Three examples are presented to validate this technique, and very close agreement is shown to exist between this method and the full electromagnetic analysis using the far field antenna radiation patterns.

This work concentrates on the application of diversity techniques and space time block coding for future mobile wireless communications. The initial system analysis employs a space-time coded OFDM transmitter over a multipath Rayleigh channel, and a receiver which uses a selection combining diversity technique. The performance of this combined scenario is characterised in terms of the bit error rate and throughput. A novel four element QOSTBC scheme is introduced, it is created by reforming the detection matrix of the original QOSTBC scheme, for which an orthogonal channel matrix is derived. This results in a computationally less complex linear decoding scheme as compared with the original QOSTBC. Space time coding schemes for three, four and eight transmitters were also derived using a Hadamard matrix. The practical optimization of multi-antenna networks is studied for realistic indoor and mixed propagation scenarios. The starting point is a detailed analysis of the throughput and field strength distributions for a commercial dual band 802.11n MIMO radio operating indoors in a variety of line of sight and non-line of sight scenarios. The physical model of the space is based on architectural schematics, and realistic propagation data for the construction materials. The modelling is then extended and generalized to a multi-storey indoor environment, and a large mixed site for indoor and outdoor channels based on the Bradford University campus. The implications for the physical layer are also explored through the specification of antenna envelope correlation coefficients. Initially this is for an antenna module configuration with two independent antennas in close proximity. An operational method is proposed using the scattering parameters of the system and which incorporates the intrinsic power losses of the radiating elements. The method is extended to estimate the envelope correlation coefficient for any two elements in a general (N,N) MIMO antenna array. Three examples are presented to validate this technique, and very close agreement is shown to exist between this method and the full electromagnetic analysis using the far field antenna radiation patterns.

La propagation de signaux optiques à travers des milieux diffusants ou multimodes est un problème largement étudié dans la communauté scientifique. De nombreuses études ont été conduites dans le but de développer des méthodes efficaces pour la reconstruction d'information après une propagation ayant modifié le contenu envoyé. De telles études font échos à de nombreux domaines d'applications, comme les télécommunications optiques ou l'endoscopie en biologie. Dans ce but, de nombreuses approches ont été envisagées dans les dernières années. Certaines s'appuient sur l'utilisation de cristaux photoréfractifs, de valves optiques, et de plus en plus largement sur des techniques d'holographie numérique basées sur l'utilisation de modulateurs spatiaux de lumière.Pendant ma thèse, j'ai développé une nouvelle approche sur l'étude et la manipulation des propriétés de cohérence spatio-temporelle d'un faisceau après propagation à travers un fibre multimode. Cette méthode s'appuie sur une interaction de mélange à deux onde opto-numérique, reposant sur l'utilisation combinée d'une caméra et d'un modulateur spatial de lumière. Cette étude découle d'expériences de mélange à deux ondes initialement réalisées dans des milieux photoréfractifs. Mais contrairement à ces expériences, les paramètres intervenant dans cette expérience ne sont pas soumis aux propriétés intrinsèques du matériau et permet ainsi une plus grande flexibilité quant à la manipulation des propriétés de cohérence spatio-temporelle du signal
Propagation of optical signals through multimode scattering media is a very fundamental problem in physics. Many studies have been conducted in order to find efficient methods for the reconstruction of information from a scrambled content. Applications range from telecommunication information retrievement to biological endoscopy. In these goals, various approaches have been developed in the past few years. Some are based on two-wave mixing interaction in photorefractive crystals, others use light valves or numerical holography based on a spatial light modulator.During my PhD, I designed a new method for the study of spatio-temporal properties of optical information that has been scrambled through a multimode medium. This method relies on a digitally assisted two-wave mixing interaction based on a camera - Spatial light modulator combination. This study ensues from signal manipulation with a photorefractive crystal experiment. Besides, experimental parameters are not limited by the intrinsic properties of a crystal and allows much more flexibility on the light manipulation

Dans le contexte d’une demande croissante de débits de communications de plus en plus élevés, les systèmes multiporteuses ont suscité un grand intérêt dans la communauté scientifique depuis ces dernières années et sont désormais employées dans de nombreux systèmes de communication. Malheureusement, ce type de système est extrêmement sensible aux distorsions de phase, comme le bruit de phase et le décalage fréquentiel de la porteuse, engendrées par l’instabilité des oscillateurs locaux. Le but de cette thèse est donc de concevoir un récepteur capable de compenser ces perturbations. Notre approche à ce problème non-linéaire est basée sur l’inférence Bayésienne et plus particulièrement sur les méthodes séquentielles de Monte-Carlo, appelées également filtrage particulaire. En premier lieu, nous proposons un estimateur conjoint du canal et des distorsions de phase grâce à une séquence d’apprentissage. Ensuite, nous traitons le problème de l’estimation des données en présence de distorsions de phase. Les filtres particulaires proposés sont implémentés efficacement en combinant le principe d’échantillonnage par importance, un schéma de sélection, une technique de réduction de variance d’estimée et surtout un nouvel estimateur “on-line” de paramètres utilisant des algorithmes d’espérance-maximisation stochastique parallèles. De plus, dans le but toujours d’augmenter l’efficacité et la robustesse de nos estimateurs, nous proposons une modélisation originale du signal multiporteuses dans le domaine temporel par un processus autorégréssif dans le cas où des porteuses nulles ou pilotes sont présentes
Multicarrier transmission systems have aroused great interest in recent years as a potential solution to the problem of transmitting high data rate over a frequency selective fading channel. Nowadays, multicarrier modulation is being selected as the transmission scheme for the majority of new communication systems. However, multicarrier systems are very sensitive to phase noise and carrier frequency offset caused by the oscillator instabilities. In this thesis, a general receiver for compensating the phase distortions effects in multicarrier systems is proposed. Our approach to this non-linear problem is based on Bayesian inference using sequential Monte Carlo filtering also referred to as particle filtering. First, the problem of channel estimation in the presence of phase noise and carrier frequency offset is addressed. Then, a particle filter is proposed to include the joint signal, phase noise and carrier frequency offset estimation. The proposed sequential Monte Carlo filters are efficiently implemented by combining sequential importance sampling, a selection scheme, a variance reduction technique and especially a new on-line parameter estimation based on parallel stochastic expectation maximization algorithms. Moreover in order to improve the estimation accuracy, an original autoregressive modeling of the time-domain multicarrier signal including either pilot or null-subcarriers is also proposed. Extensive simulation study is provided to illustrate the efficiency and the robustness of the proposed algorithms in comparison with those of existing schemes

Single Carrier Frequency Division Multiple Access (SC-FDMA) is a multiple access transmission scheme that has been adopted in the 4th generation 3GPP Long Term Evolution (LTE) of cellular systems. In fact, its relatively low peak-to-average power ratio (PAPR) makes it ideal for the uplink transmission where the transmit power efficiency is of paramount importance. Multiple access among users is made possible by assigning different users to different sets of non-overlapping subcarriers. With the current LTE specifications, if an SC-FDMA system is operating at its full capacity and a new user requests channel access, the system redistributes the subcarriers in such a way that it can accommodate all of the users. Having less subcarriers for transmission, every user has to increase its modulation order (for example from QPSK to 16QAM) in order to keep the same transmission rate. However, increasing the modulation order is not always possible in practice and may introduce considerable complexity to the system. The technique presented in this thesis report describes a new way of adding more users to an SC-FDMA system by assigning the same sets of subcarriers to different users. The main advantage of this technique is that it allows the system to accommodate more users than conventional SC-FDMA and this corresponds to increasing the spectral efficiency without requiring a higher modulation order or using more bandwidth. During this work, special attentions wee paid to the cases where two and three source signals are being transmitted on the same set of subcarriers, which leads respectively to doubling and tripling the spectral efficiency. Simulation results show that by using the proposed technique, it is possible to add more users to any SC-FDMA system without increasing the bandwidth or the modulation order while keeping the same performance in terms of bit error rate (BER) as the conventional SC-FDMA. This is realized by slightly increasing the energy per bit to noise power spectral density ratio (Eb/N0) at the transmitters.

碩士
國立成功大學
電腦與通信工程研究所
104
Massive MIMO is one of the important technologies in 5G mobile communication system development. System can get much spectrum efficiency improvement by placing a great number of antennas at base station (BS) and using liner precoding scheme (ex. Zero-Forcing Precoding). But, in practice, base station needs the channel state information (CSI) from all users to carry out the liner precoding process and it will cause dramatic feedback overhead in FDD systems. Previous literature proposed a Joint Spatial Division and Multiplexing (JSDM) precoding scheme, which combined the prebeamforming and conventional Zero-Forcing precoding, to reduce CSI feedback overhead and the complexity for precoding matrices computation. Most literature related to the JSDM precoding scheme usually assumed that all users in the same group or same beam have identical antenna correlation matrices and design the prebeamforming matrices based on this assumption. But in real communication scenario, users have different antenna correlation matrices even in same the group due to their different geographic locations. Hence, user grouping algorithm based on the similarity between the antenna correlation matrices becomes an important issue in JSDM precoding scheme. In this thesis, the user grouping algorithms for the JSDM precoding scheme with both the adaptive prebeamforming and fixed prebeamforming schemes are studied and proposed to apply on the practical user distribution scenario. The numerical results show the comparison of the performance and complexity among different grouping algorithms.

Traditional OFDM implementations use conventional Fourier filters for data modulation, via the IFFT operation. Much research suggests wavelet based OFDM provides performance gains, due to superior spectral containment properties of wavelet filters. When compared in simulation, neither system was found fundamentally better than the other. Rather than focus on filter bank design, joint detection strategies provide a relatively simple method for improving system performance. The conventional matched filter used in OFDM systems, is only optimal when the channel introduces no carrier distoration. We propose an optimal detector, which maximizes the probability of making correct decisions, and a suboptimal method which decorrelates carriers based on knowledge of the channel. Both joint detection methods provide significant performance gains in OFDM systems over conventional matched filtering.

碩士
國立臺灣科技大學
電機工程系
107
Spatial Modulation(SM) is one of the most adopted Multiple-Input Multiple-Output(MIMO) techniques in recent years. Its characteristics are only activating one single antenna at the same time, antenna index and transmitted symbol and both being used by the transmission bit. The intention is to increase the spectral efficiency and energy efficiency, there are many other MIMO techniques have been proposed based on the same concept, such as Generalized Spatial Modulation(GSM), Space Shift Keying(SSK), Space Time Shift Keying(STSK) and so on. Generalized Spatial Modulation is an extended version of Spatial Modulation, it activated more than one antenna at the same time, using number of combinations of different antennas, which makes the antenna number no longer has to be limited by the power of two. Generalized Spatial Modulation has more flexibility than original Spatial Modulation. In this thesis, we adopt Orthogonal Frequency Division Multiplexing(OFDM) which is widely used in wireless communication systems and Single Carrier Frequency Division Multiple Access(SC-FDMA) proposed by LTE-A, which adopt Discrete Fourier Transform (DFT) as a precoding scheme and known for its low Peak to Average Power Ratio (PAPR) characteristic as the uplink system. We combine these two systems with GSM, in order to have better bit error rate(BER) and spectral efficiency. In this thesis, we discussed combinations of Spatial Modulation with OFDM and SC-FDMA and proposed GSM-OFDM and GSM-SCFDMA. We will simulate all the systems BER performance in different number antenna case and modulation type through different channel model. Also we discussed the PAPR performance after adding SM and GSM.

碩士
國立成功大學
資訊工程學系
107
In SDM-EONs, routing, core, modulation format, and spectrum assignment (RCMSA) is a critical issue. In this thesis, we consider RCMSA problem with two types of traffic demands; one is the category of requests which need to be served immediately (immediate reservation; IR) and the other is the kind of request that can be reserved in advance (advance reservation; AR). In previous literature, a partition-based resource management method has been proposed. It claims to divide the spectral resource into several prioritized areas and to each one is dedicated request with specific size. However, the method suffers some drawbacks. First, all possible sizes of requests are known a priori to divide the spectrum resources. The next one is the sizes of prioritized areas is predetermined but inadequate size might deteriorate the blocking performance. The last one is this partition-based method may consume a lot of searching time. Therefore, we used another resource management concept called clustering and propose several cluster-based algorithms to solve RCMSA problem. In simulation results, BBP of our proposed method CB-KF-N-KL-C can achieve about 40%~99% improvement in JPN-12 and 45%~90% in US backbone as compared with partition-based scheme. In the aspect of execution efficiency, the performance gain can reach about 50%~65% improvement in both JPN-12 and US backbone with 8 cores per fiber link.

The integration of Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques has become a preferred solution for the high rate wireless technologies due to its high spectral efficiency, robustness to frequency selective fading, increased diversity gain, and enhanced system capacity. The main drawback of OFDM-based systems is their susceptibility to impairments such as Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), Symbol Timing Error (STE), Phase Noise (PHN), and fading channel. These impairments, if not properly estimated and compensated, degrade the performance of the OFDM-based systems In this thesis, a system model for MIMO-OFDM that takes into account the effects of all these impairments is formulated. Using this system model, we de-rive Cramer-Rao Lower Bounds (CRLBs) for the joint estimation of deterministic impairments in MIMO-OFDM system, which show the coupling effect among different impairments and the significance of the joint estimation. Also, Bayesian CRLBs for the joint estimation of random impairments in OFDM system are derived. Similarly, we derive Hybrid CRLBs for the joint estimation of random and deterministic impairments in OFDM system, which show the significance of using Bayesian approach in estimation. Further, we investigate different algorithms for the joint estimation of all impairments in OFDM-based system. Maximum Likelihood (ML) algorithms and its low complexity variants, for the joint estimation of CFO, SFO, STE, and channel in MIMO-OFDM system, are proposed. We propose a low complexity ML algorithm which uses Compressed Sensing (CS) based channel estimation method in a sparse fading sce-nario, where the received samples used for estimation are less than that required for a Least Squares (LS) or Maximum a posteriori (MAP) based estimation. Also, we propose MAP algorithms for the joint estimation of the random impairments, PHN and channel, utilizing their statistical knowledge which is known a priori. Joint estimation algorithms for SFO and channel in OFDM system, using Bayesian framework, are also proposed in this thesis. The performance of the estimation methods is studied through simulations and numerical results show that the performance of the proposed algorithms is better than existing algorithms and is closer to the derived CRLBs.

The integration of Multiple Input Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques has become a preferred solution for the high rate wireless technologies due to its high spectral efficiency, robustness to frequency selective fading, increased diversity gain, and enhanced system capacity. The main drawback of OFDM-based systems is their susceptibility to impairments such as Carrier Frequency Offset (CFO), Sampling Frequency Offset (SFO), Symbol Timing Error (STE), Phase Noise (PHN), and fading channel. These impairments, if not properly estimated and compensated, degrade the performance of the OFDM-based systems In this thesis, a system model for MIMO-OFDM that takes into account the effects of all these impairments is formulated. Using this system model, we de-rive Cramer-Rao Lower Bounds (CRLBs) for the joint estimation of deterministic impairments in MIMO-OFDM system, which show the coupling effect among different impairments and the significance of the joint estimation. Also, Bayesian CRLBs for the joint estimation of random impairments in OFDM system are derived. Similarly, we derive Hybrid CRLBs for the joint estimation of random and deterministic impairments in OFDM system, which show the significance of using Bayesian approach in estimation. Further, we investigate different algorithms for the joint estimation of all impairments in OFDM-based system. Maximum Likelihood (ML) algorithms and its low complexity variants, for the joint estimation of CFO, SFO, STE, and channel in MIMO-OFDM system, are proposed. We propose a low complexity ML algorithm which uses Compressed Sensing (CS) based channel estimation method in a sparse fading sce-nario, where the received samples used for estimation are less than that required for a Least Squares (LS) or Maximum a posteriori (MAP) based estimation. Also, we propose MAP algorithms for the joint estimation of the random impairments, PHN and channel, utilizing their statistical knowledge which is known a priori. Joint estimation algorithms for SFO and channel in OFDM system, using Bayesian framework, are also proposed in this thesis. The performance of the estimation methods is studied through simulations and numerical results show that the performance of the proposed algorithms is better than existing algorithms and is closer to the derived CRLBs.

Orthogonal frequency-division multiplexing (OFDM) has been adopted by many broadband wireless communication systems for the simplicity of the receiver technique to support high data rates and user mobility. However, studies also show that the advantage of OFDM over the single-carrier modulation schemes could be substantially compromised by timing or frequency estimation errors at the receiver. In this thesis we investigate the synchronization problem for practical OFDM systems using a system model generalized from the IEEE 802.11 and IEEE 802.16 standards. For preamble based synchronization schemes, which are most common in the downlink of wireless communication systems, we propose a novel timing acquisition algorithm which minimizes false alarm probability and indirectly improves correct detection probability. We then introduce a universal fractional carrier frequency offset (CFO) estimator that outperforms conventional methods at low signal to noise ratio with lower complexity. More accurate timing and frequency estimates can be obtained by our proposed frequency-domain algorithms incorporating channel knowledge. We derive four joint frequency, timing, and channel estimators with different approximations, and then propose a hybrid integer CFO estimation scheme to provide flexible performance and complexity tradeoffs. When the exact channel delay profile is unknown at the receiver, we present a successive timing estimation algorithm to solve the timing ambiguity. Both analytical and simulation results are presented to confirm the performance of the proposed methods in various realistic channel conditions. ...

Bayesian approaches for sparse signal recovery have enjoyed a long-standing history in signal processing and machine learning literature. Among the Bayesian techniques, the expectation maximization based Sparse Bayesian Learning(SBL) approach is an iterative procedure with global convergence guarantee to a local optimum, which uses a parameterized prior that encourages sparsity under an evidence maximization frame¬work. SBL has been successfully employed in a wide range of applications ranging from image processing to communications. In this thesis, we propose novel, efficient and low-complexity SBL-based algorithms that exploit structured sparsity in the presence of fully/partially known measurement matrices. We apply the proposed algorithms to the problem of channel estimation and data detection in Orthogonal Frequency Division Multiplexing(OFDM) systems. Further, we derive Cram´er Rao type lower Bounds(CRB) for the single and multiple measurement vector SBL problem of estimating compressible vectors and their prior distribution parameters. The main contributions of the thesis are as follows: We derive Hybrid, Bayesian and Marginalized Cram´er Rao lower bounds for the problem of estimating compressible vectors drawn from a Student-t prior distribution. We derive CRBs that encompass the deterministic or random nature of the unknown parameters of the prior distribution and the regression noise variance. We use the derived bounds to uncover the relationship between the compressibility and Mean Square Error(MSE) in the estimates. Through simulations, we demonstrate the dependence of the MSE performance of SBL based estimators on the compressibility of the vector. OFDM is a well-known multi-carrier modulation technique that provides high spectral efficiency and resilience to multi-path distortion of the wireless channel It is well-known that the impulse response of a wideband wireless channel is approximately sparse, in the sense that it has a small number of significant components relative to the channel delay spread. In this thesis, we consider the estimation of the unknown channel coefficients and its support in SISO-OFDM systems using a SBL framework. We propose novel pilot-only and joint channel estimation and data detection algorithms in block-fading and time-varying scenarios. In the latter case, we use a first order auto-regressive model for the time-variations, and propose recursive, low-complexity Kalman filtering based algorithms for channel estimation. Monte Carlo simulations illustrate the efficacy of the proposed techniques in terms of the MSE and coded bit error rate performance. • Multiple Input Multiple Output(MIMO) combined with OFDM harnesses the inherent advantages of OFDM along with the diversity and multiplexing advantages of a MIMO system. The impulse response of wireless channels between the Nt transmit and Nr receive antennas of a MIMO-OFDM system are group approximately sparse(ga-sparse),i.e. ,the Nt Nr channels have a small number of significant paths relative to the channel delay spread, and the time-lags of the significant paths between transmit and receive antenna pairs coincide. Often, wire¬less channels are also group approximately-cluster sparse(ga-csparse),i.e.,every ga-sparse channel consists of clusters, where a few clusters have all strong components while most clusters have all weak components. In this thesis, we cast the problem of estimating the ga-sparse and ga-csparse block-fading and time-varying channels using a multiple measurement SBL framework. We propose a bouquet of novel algorithms for MIMO-OFDM systems that generalize the algorithms proposed in the context of SISO-OFDM systems. The efficacy of the proposed techniques are demonstrated in terms of MSE and coded bit error rate performance.

Bayesian approaches for sparse signal recovery have enjoyed a long-standing history in signal processing and machine learning literature. Among the Bayesian techniques, the expectation maximization based Sparse Bayesian Learning(SBL) approach is an iterative procedure with global convergence guarantee to a local optimum, which uses a parameterized prior that encourages sparsity under an evidence maximization frame¬work. SBL has been successfully employed in a wide range of applications ranging from image processing to communications. In this thesis, we propose novel, efficient and low-complexity SBL-based algorithms that exploit structured sparsity in the presence of fully/partially known measurement matrices. We apply the proposed algorithms to the problem of channel estimation and data detection in Orthogonal Frequency Division Multiplexing(OFDM) systems. Further, we derive Cram´er Rao type lower Bounds(CRB) for the single and multiple measurement vector SBL problem of estimating compressible vectors and their prior distribution parameters. The main contributions of the thesis are as follows: We derive Hybrid, Bayesian and Marginalized Cram´er Rao lower bounds for the problem of estimating compressible vectors drawn from a Student-t prior distribution. We derive CRBs that encompass the deterministic or random nature of the unknown parameters of the prior distribution and the regression noise variance. We use the derived bounds to uncover the relationship between the compressibility and Mean Square Error(MSE) in the estimates. Through simulations, we demonstrate the dependence of the MSE performance of SBL based estimators on the compressibility of the vector. OFDM is a well-known multi-carrier modulation technique that provides high spectral efficiency and resilience to multi-path distortion of the wireless channel It is well-known that the impulse response of a wideband wireless channel is approximately sparse, in the sense that it has a small number of significant components relative to the channel delay spread. In this thesis, we consider the estimation of the unknown channel coefficients and its support in SISO-OFDM systems using a SBL framework. We propose novel pilot-only and joint channel estimation and data detection algorithms in block-fading and time-varying scenarios. In the latter case, we use a first order auto-regressive model for the time-variations, and propose recursive, low-complexity Kalman filtering based algorithms for channel estimation. Monte Carlo simulations illustrate the efficacy of the proposed techniques in terms of the MSE and coded bit error rate performance. • Multiple Input Multiple Output(MIMO) combined with OFDM harnesses the inherent advantages of OFDM along with the diversity and multiplexing advantages of a MIMO system. The impulse response of wireless channels between the Nt transmit and Nr receive antennas of a MIMO-OFDM system are group approximately sparse(ga-sparse),i.e. ,the Nt Nr channels have a small number of significant paths relative to the channel delay spread, and the time-lags of the significant paths between transmit and receive antenna pairs coincide. Often, wire¬less channels are also group approximately-cluster sparse(ga-csparse),i.e.,every ga-sparse channel consists of clusters, where a few clusters have all strong components while most clusters have all weak components. In this thesis, we cast the problem of estimating the ga-sparse and ga-csparse block-fading and time-varying channels using a multiple measurement SBL framework. We propose a bouquet of novel algorithms for MIMO-OFDM systems that generalize the algorithms proposed in the context of SISO-OFDM systems. The efficacy of the proposed techniques are demonstrated in terms of MSE and coded bit error rate performance.

The increasing demand for high data rate transmission over broadband radio channels has imposed significant challenges in wireless communications. Accurate channel estimation has a major impact on the whole system performance. Specifically, reliable estimate of the channel state information (CSI) is more challenging for orthogonal frequency division multiplexing (OFDM) systems in doubly selective fading channels than for the slower fading channels over which OFDM has been deployed traditionally. With the help of a basis expansion model (BEM), a novel multivariate autoregressive (AR) process is developed to model the time evolution of the fast fading channel. Relying on pilot symbol aided modulation (PSAM), a novel Kalman smoothing algorithm based on a second-order dynamic model is exploited, where the mean square error (MSE) of the channel estimator is near to that of the optimal Wiener filter. To further improve the performance of channel estimation, a novel low-complexity iterative joint channel estimation and symbol detection procedure is developed for fast fading channels with a small number of pilots and low pilot power to achieve the bit error rate (BER) performance close to when the CSI is known perfectly. The new channel estimation symbol detection technique is robust to variations of the radio channel from the design values and applicable to multiple modulation and coding types. By use of the extrinsic information transfer (EXIT) chart, we investigate the convergence behavior of the new algorithm and analyze the modulation, pilot density, and error correction code selection for good system performance for a given power level. The algorithms developed in this thesis improve the performance of the whole system requiring only low ratios of pilot to data for excellent performance in fast fading channels.
Graduate

Current transport optical networks are approaching its capacity limits, mainly due to new applications and services that require a huge amount of resources. To increase the network capacity, multiband solutions, that exploit the unused capacity of actual fibers, in particular the L-band, are being currently commercially explored. However, this strategy is assumed as a short to medium term solution. A long-term solution is to use spatial-division multiplexing (SDM) in the optical domain, which leads to the concept of SDM-based optical networks. In this work, different SDM switching architectures (spatial, spatial-wavelength, wavelength, fractional space-full wavelength) are studied and compared in terms of cost per bit, power consumption and flexibility. For the switching architectures with spatial and spatial-wavelength granularities (the architectures that have superior performance), the most relevant physical impairments (PLIs) (amplifiers noise, non-linear interference, narrowing penalty due to filtering and in-band crosstalk) are analytically studied, for a SDM reconfigurable optical add-drop multiplexer (ROADM) cascade. Furthermore, a Monte Carlo simulation is used to assess more rigorously the PLIs effects on the performance of SDM ROADMs, with spatial-wavelength switching architecture, in cascade. The main difference, regarding PLIs, between the single spatial channel ROADM architecture and the SDM ROADM architectures is the enhanced effect of in-band crosstalk. For cascaded ROADMs with 16 directions, 19 spatial channels and filtering isolation of -25 dB, the in-band crosstalk can lead to a 2 dB optical signal-to-noise ratio penalty. Due to this penalty, the signal crosses less 9 ROADMs than in a single spatial channel ROADM architecture.
As redes óticas de transporte atuais estão a aproximar-se do seu limite de capacidade devido às novas aplicações e serviços que requerem uma maior quantidade de recursos de rede. Uma possível solução de curto a médio prazo para a falta de recursos é o uso de múltiplas bandas da fibra, para além da banda C. Uma solução a longo prazo será o uso de multiplexagem com divisão no espaço (SDM) no domínio óptico. Neste trabalho são estudados, o custo por bit, consumo de energia e flexibilidade, das diferentes arquiteturas SDM (no espaço, no espaço e comprimento de onda, no comprimento de onda, fracionada no espaço e completa no comprimento de onda). Para as arquiteturas com granularidades no espaço e no espaço e comprimento de onda estuda-se analiticamente os efeitos das principais limitações do nível físico (PLIs) (ruído dos amplificadores, interferência não-linear, penalidade de filtragem e diafonia homódina), para cascatas de multiplexadores óticos de inserção/extração reconfiguráveis (ROADMs). Usa-se uma simulação Monte Carlo para calcular mais rigorosamente os efeitos das PLIs na arquitetura com granularidade no espaço e comprimento de onda. A principal diferença, em termos de PLIs, entre uma rede SDM e uma rede com um único canal espacial é o efeito da diafonia homódina. Para uma rede com 16 direções, 19 canais espaciais e isolamento dos filtros de -25 dB, a diafonia homódina causa uma penalidade na relação sinal-ruído óptica de 2 dB e o sinal atravessa menos 9 ROADMs que numa rede com apenas um canal espacial.